Update wasmi_ir2::BranchOffset type (#1661)

update BranchOffset type

Author: Robbepop

crates/ir2/src/encode.rs

@@ -87,7 +87,7 @@ impl Encode for BranchOffset {
     where
         E: Encoder,
     {
-        let pos = self.to_i32().encode(encoder)?;
+        let pos = i32::from(*self).encode(encoder)?;
         encoder.branch_offset(pos, *self)?;
         Ok(pos)
     }

crates/ir2/src/error.rs

@@ -5,8 +5,6 @@ use core::fmt;
 pub enum Error {
     /// Encountered when trying to create a [`Slot`](crate::Slot) from an out of bounds integer.
     StackSlotOutOfBounds,
-    /// Encountered when trying to create a [`BranchOffset`](crate::BranchOffset) from an out of bounds integer.
-    BranchOffsetOutOfBounds,
     /// Encountered when trying to create a [`BlockFuel`](crate::BlockFuel) from an out of bounds integer.
     BlockFuelOutOfBounds,
     /// Encountered when trying to create a [`Memory`] from an out of bounds integer.
@@ -19,7 +17,6 @@ impl fmt::Display for Error {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         let s = match self {
             Self::StackSlotOutOfBounds => "stack slot out of bounds",
-            Self::BranchOffsetOutOfBounds => "branch offset out of bounds",
             Self::BlockFuelOutOfBounds => "block fuel out of bounds",
             Self::MemoryIndexOutOfBounds => "memory index out of bounds",
         };

crates/ir2/src/primitive.rs

@@ -106,35 +106,31 @@ impl From<i32> for BranchOffset {
     }
 }
 
+impl From<BranchOffset> for i32 {
+    fn from(offset: BranchOffset) -> Self {
+        offset.0
+    }
+}
+
 impl BranchOffset {
-    /// Creates an uninitialized [`BranchOffset`].
-    pub fn uninit() -> Self {
-        Self(0)
+    /// Returns `true` if [`Self`] is an offset for a backward branch.
+    pub fn is_backwards(&self) -> bool {
+        self.0.is_negative()
     }
 
-    /// Creates an initialized [`BranchOffset`] from `src` to `dst`.
-    ///
-    /// # Errors
-    ///
-    /// If the resulting [`BranchOffset`] is out of bounds.
-    pub fn from_src_to_dst(src: u32, dst: u32) -> Result<Self, Error> {
-        let src = i64::from(src);
-        let dst = i64::from(dst);
-        let Some(offset) = dst.checked_sub(src) else {
-            // Note: This never needs to be called on backwards branches since they are immediated resolved.
-            unreachable!(
-                "offset for forward branches must have `src` be smaller than or equal to `dst`"
-            );
-        };
-        let Ok(offset) = i32::try_from(offset) else {
-            return Err(Error::BranchOffsetOutOfBounds);
-        };
-        Ok(Self(offset))
+    /// Returns `true` if [`Self`] is an offset for a forward branch.
+    pub fn is_forwards(&self) -> bool {
+        self.0.is_positive()
     }
 
     /// Returns `true` if the [`BranchOffset`] has been initialized.
     pub fn is_init(self) -> bool {
-        self.to_i32() != 0
+        self.0 != 0
+    }
+
+    /// Creates an uninitialized [`BranchOffset`].
+    pub fn uninit() -> Self {
+        Self(0)
     }
 
     /// Initializes the [`BranchOffset`] with a proper value.
@@ -148,11 +144,6 @@ impl BranchOffset {
         assert!(!self.is_init());
         *self = valid_offset;
     }
-
-    /// Returns the `i32` representation of the [`BranchOffset`].
-    pub fn to_i32(self) -> i32 {
-        self.0
-    }
 }
 
 /// The accumulated fuel to execute a block via [`Op::ConsumeFuel`].